Composite elongate member having a predetermined effective coefficient of linear expansion

ABSTRACT

A stator shroud ring assembly in which a turbine of a gas turbine engine is positioned with an annular gap of predetermined radial distance between the stator shroud ring and the periphery of the turbine rotor, the stator shroud ring assembly including a stator shroud ring constructed from at least one arcuate portion made of one material and at least one arcuate portion made of another material, the co-efficients of linear expansion of the materials employed and the total arcuate length employed of each material being such that the circumferential length of whole shroud ring will change with temperature by an amount corresponding to a predetermined effective co-efficient of linear expansion substantially equal to that of the rotor material.

Penny COMPOSITE ELONGATE MEMBER HAVING A PREDETERMINED EFFECTIVECOEFFICIENT OF LINEAR EXPANSION [76] Inventor: Robert Noel Penny, 12Alderbrook Rd., Solihull, England [22] Filed: Nov. 27, 1972 [21] App].No.: 309,790

[30] Foreign Application Priority Data Dec. 1, 1971 Great Britain55665/71 [52] US. Cl 415/197, 415/214, 415/219 R [51] Int. Cl. F04d19/00, F04d 29/02 [58] Field of Search 418/134, 136; 415/214,

[56] References Cited UNITED STATES PATENTS 2,555,256 5/1951 Tyson415/214 2,863,634 12/1958 Chamberlin et al.... 415/134 2,962,256 11/1960Bishop 1 415/136 3,085,398 4/1963 Ingleson 60/3932 3,430,898 3/1969Parechanian et a1. 415/214 Dec. 17, 1974 FOREIGN PATENTS OR APPLICATIONS1,247,283 10/1960 France 416/196 Primary ExaminerHenry F. RaduazoAttorney, Agent, or FirmMawhinney & Mawhinney [57 ABSTRACT A statorshroud ring assembly in which a turbine of-a gas turbine engine ispositioned with an annular gap of predetermined radial distance betweenthe stator shroud ring and the periphery of the turbine rotor,the statorshroud ring assembly including a stator shroud ring constructed from atleast one arcuate portion made of one material and at least one arcuateportion made of another material, the co-efficients of linear expansionof the materials employed and the total arcuate length employed of eachmaterial being such that the circumferential length of whole shroud ringwill change with temperature by an amount corresponding to apredetermined effective co-efficient of linear expansion substantiallyequal to that of the rotor material.

6 C1aims, 4 Drawing Figures COMPOSITE ELONGATE MEMBER HAVING APREDETERMINED EFFECTIVE COEFFICIENT OF LINEAR EXPANSION The inventionrelates to a composite elongate member having a predetermined effectivecoefficient of linear expansion and is particularly, but notexclusively, concerned with a stator shroud ring assembly to be arrangedconcentrically around a turbine rotor of a gas turbine engine.

A A stator shroud ring is provided around the periphery of a turbinerotor to define the radially outer boundary of the working fluid passagethrough the turbine. The blades of the rotor may themselves beunshrouded or they may be provided with a shroud integral with theblades and concentric with the stator shroud ring. There must ofcoursebe running clearance provided by an annular gap of a predeterminedradial thickness between the tips of the blades, where they areunshrouded, and the stator shroud ring or between the rotor shroud ring,where provided, and the stator shroud ring.

The turbine rotor, including the blades and the rotor shroud ring, whereprovided, is made of a material selected to withstand the necessary highworking temperatures. Similarly, the stator shroud ring is subjected tothe same working temperatures and is likewise made of a material capableof withstanding high temperature.

Where the rotor and the stator shroud ring are made of the samematerial, it has been found that the stator shroud ring will expand morethan the rotor and therefore the annular gap will increase in radialthickness as working temperature increases. This is because thetemperature gradient radially of the rotor increases from the hub to theblade tips or the rotor shroud ring, where provided. The increase in theradial thickness of the gap results in loss of performance when theturbine has reached its operating temperature, because there must be aminimum clearance when the turbine is cold to prevent the rotor rubbingagainst the stator shroud ring. An object of the invention is to providea stator shroud ring which'will have substantially the same radialexpansion characteristics as the rotor, thereby resulting in an annulargap between the rotor and the stator shroud ring of substantiallyuniform radial thickness throughout the range'of operating temperatureof the turbine.

According to the invention, a composite elongate member is constructedfrom at least one portion madeof one material and at least one portionmade .of an-' other material, the portions being assembled end-toend andthe co-efficients of linear expansion of the materials employed and thetotal length employed of each material being such that the whole memberwhen subjected to a temperature change will-change in length by anamount corresponding to a predetermined effective co-efficie'nt oflinear expansion,

The invention also provides a stator shroud ring assembly in which aturbine rotor of a gas turbine engine is to be positioned with anannular gap of predetermined radial distance between the stator shroudring and the periphery of the turbine rotor, the stator shroud ringassembly including a stator shroud-ring constructed from at least onearcuate portion made of one material and at least one arcuate portionmade of another material, the arcuate portions being assembledend-to-end and the co-efficients of linear expansion of efficient oflinear expansion as the nickel-based alloy; I

of the rotor, the radial dimension of the annular gap thereby beingmaintained at substantially the aforesaid predeterminedvalue.

Conveniently the stator shroud ring is formed from arcuate portions oftwo different materials but arcuate portions made of more than twomaterials may be used if desired.

Conveniently, one of the materials from whichthe arcuate portions aremade is the same as that from which the rotor is formed, the othermaterial or materials having a lower co-efficient of expansion, wherebythe effective expansion of thecomposite stator shroud ring will besubstantially the same as that of the rotor.

The arcuate portions. may have interengageable end faces.

The arcuate portions may be bounded by a concentric enveloping ring madeof a material having a co-v efficient of linear expansion substantiallythe same as the material from which the turbine rotor is formed. Thematerial of the concentric enveloping ring may have inferior stressrupture properties compared with the material from which the rotor ismade.

The invention also includes a gas turbine including a rotor and a statorshroud'ring assembly inaccordance with any one of the five immediatelypreceding paragraphs. v

By way of example, a gas turbine having a composite stator shroud ringin accordance with the invention is now described with reference to theaccompanying V drawings, in which:

FIG. 1 isan axial section through a peripheral portion of the turbine;

FIG. 2 is an end view of the turbine shown in FIG. 1;

FIG. 3 shows a modified form of the stator shroud 'ring shown in FIG. 2,and

FIG. 4 is' a view similar to FIG. 1' showing a further modification.

Referring to FIGS. 1 and 2 the turbine has a stator shroud ring formedfrom a plurality of arcuate portions l, 2 two or more abutted togethercircumferentially to 'form a complete annulus; The segmental portions 1,2

are made of 'two different materials but where there are more than twoarcuate portions more than two materials may be used. One or more of thearcuate portions 1 are made of the same material as the rotor 12, e.g.,'

a nickel-based alloy, and the other arcuate portion or portions 2 aremade of a ceramic or ceramic-like material, such as silicon nitride. Thearcuate portions are held within an enveloping concentric outer ring 3which may be made of a material having the same cobut which may be madeof a cheaper material having an inferior stress rupture property, whichitself would not be capable of withstanding the stresses to which thestator shroud ring will be subjected during operation of the turbine.The ratio of the total circumferential length of the arcuate portions2t0 the total circumferential length of the alloy portions 1 is suchthat the effective co-efficient of linear expansion of the compositestator shroud ring is substantially equal to the coefficient of linearexpansion of the material of the rotor. For example, where the relativeco-efficient of linear expansion of the alloy is 18 and the relativecoefficient of linear expansion of the ceramic material is 3 andthethermal gradient radially of the turbine rotor results in theeffective relative co-efficient of linear expansion of the rotor being12, the effective relative coefficient of linear expansion of thecomposite stator ring could also be made to be 12 by making the ratio ofthe circumferential lengths of the alloy to ceramic segmental portionsin the ratio of 3:2.

By making the effective linear co-efficient of expansion of thecomposite stator shroud ring substantially equal to the co-efficient oflinear expansion of the ma terial from which the rotor is made, theradial dimension of the gap X between the stator shroud ring and thetips of the rotor blades, or the rotor blade shroud ring, whereprovided, is maintained substantially constant over the range ofoperating temperatures for which the turbine has been designed.

The external concentric envelopingring 3 may be located from movement inthe axial direction by clamping it between two housing parts 4 and 5,such as the nozzle guide vane supporting ring'and another annular shroudpositioned between the turbine rotor and an adjacent rotor. The ring 3may make a shrink fit in one or both of the housing parts.

The composite shroud ring 1, 2 may extend over a ring of nozzle guidevanes as well as the rotor blades.

As shown in FlG. 2, the arcuate portions 1, 2 may have interengagingends, such as ribs and notches 6 to maintain correct relative locationof the portions. Al-

ternatively the opposite circumferential ends of each of 7 the portionsmay be made concave and convex respectively as shown at 7 in FIG. 3.This construction would also maintain adjacent ends of theportions atthe correct radial locations.

FIG. 4 shows a modification of the construction I shown in FIG. 2 inwhich the concentric enveloping ring 8 is tapered in the axial directionand is engaged with a frusto-conical face of a housing member 9. Aspring 10 acts betwen the ring 8 and a second housing member 1 l andthereby urges the ring 8 by wedging ac-- tion radially inwardly againstthe composite: ring 1, 2. Hence the arcuate portions 1, 2 will bemaintained in end-to-end abutment.

What I claim as my invention and desire to secure by Letters Patent ofthe United States is:

1. A stator shroud ring assembly in which a turbine of a gas turbineengine is to be positioned with an annular gap of predetermined radialdistance between the stator shroud ring and the periphery of the turbinerotor, the stator shroud ring assembly including a stator shroud ringconstructed from at least one arcuate portion made of one material andat least one arcuate portion made of another material, the arcuateportions being assembled ,end-to-end and the co-efficients of linearexpansion of the material employed and the total arcuate length employedof each material'being such that the circumferential length of the wholeshroud ring will change with temperature, within the range of workingtemperature for which the engine has been designed, by an amountcorresponding to a predetermined effective cO-efficient of linearexpansion, whereby the total change in circumferential length of thestator shroud ring will substantially correspond to the alteration indiameter of the rotor, the radial dimension of said annular gap therebybeing maintained at substantially the aforesaid predetemiined value.

2. A stator shroud ring assembly as claimed in claim 1 in whichthestator shroud ring is formed from arcuate portions of two differentmaterials.

3. A stator shroud ring assembly as claimed in claim 1 in which one ofthe materials from which the arcuate portions are made is the same asthat from which the rotor is formed, the material of the remainingarcuate portions having a lowerco-efficient of expansion,

whereby the effective expansion of the composite stator shroud ring issubstantially the same as that of the rotor.

4'. A stator shroud ring assembly as claimed in claim 1 in which thearcuate portions have interengageable end faces. I

5. A stator shroud ring assembly as claimed in claim 1 in which aconcentric enveloping ring made of a material having a co-efiicient oflinear expansion substantially the same as the material from which theturbine rotor is made bounds the arcuate portions of the stator shroudring.

6. A gas turbine engine including a bladed turbine rotor and a statorshroud ring assembly, the latter defining a stator shroud ringsurrounding the rotor with an annular gap of predetermined radialdistance between the stator shroud ring and the periphery of the turbinerotor, the stator shroud ringbeing constructed from at least one arcuateportion made of one material and at least one arcuate portion madeofanother material, the arcuate portions being assembled end-to-end andtheco-efficients of linearexpansion of the materials employed and the totalarcuate length employed of each material being such that thecircumferential responding to a predetermined effective c'o-efficient oflinear expansion, whereby the total change in circumferential length ofthe stator shroud ring will substantially correspond to the alterationin diameter of the rotor, the radial dimension of said annular gapthereby being maintained at substantially the aforesaid predeterminedvalue.

1. A stator shroud ring assembly in which a turbine of a gas turbineengine is to be positioned with an annular gap of predetermined radialdistance between the stator shroud ring and the periphery of the turbinerotor, the stator shroud ring assembly including a stator shroud ringconstructed from at least one arcuate portion made of one material andat least one arcuate portion made of another material, the arcuateportions being assembled end-to-end and the co-efficients of linearexpansion of the material employed and the total arcuate length employedof each material being such that the circumferential length of the wholeshroud ring will change with temperature, within the range of workingtemperature for which the engine has been designed, by an amountcorresponding to a predetermined effective co-efficient of linearexpansion, whereby the total change in circumferential length of thestator shroud ring will substantially correspond to the alteration indiameter of the rotor, the radial dimension of said annular gap therebybeing maintained at substantially the aforesaid predetermined value. 2.A stator shroud ring assembly as claimed in claim 1 in which the statorshroud ring is formed from arcuate portions of two different materials.3. A stator shroud ring assembly as claimed in claim 1 in which one ofthe materials from which the arcuate portions are made is the same asthat from which the rotor is formed, the material of the remainingarcuate portions having a lower co-efficient of expansion, whereby theeffective expansion of the composite stator shroud ring is substantiallythe same as that of the rotor.
 4. A stator shroud ring assembly asclaimed in claim 1 in which the arcuate portions have interengageableend faces.
 5. A stator shroud ring assembly as claimed in claim 1 inwhich a concentric enveloping ring made of a material having aco-efficient of linear expansion substantially the same as the materialfrom which the turbine rotor is made bounds the arcuate portions of thestator shroud ring.
 6. A gas turbine engine including a bladed turbinerotor and a stator shroud ring assembly, the latter defining a statorshroud ring surrounding the rotor with an annular gap of predeterminedradial distance between the stator shroud ring and the periphery of theturbine rotor, the stator shroud ring being constructed from at leastone arcuate portion made of one material and at least one arcuateportion made of another material, the arcuate portions being assembledend-to-end and the co-efficients of linear expansion of the materialsemployed and the total arcuate length employed of each material beingsuch that the circumferential length of the whole shroud ring willchange with temperature, within the range of working temperature forwhich the engine has been designed, by an amount corresponding to apredetermined effective co-efficient of linear expansion, whereby thetotal change in circumferential length of the stator shroud ring willsubstantially correspond to the alteration in diameter of the rotor, theradial dimension of said annular gap thereby being maintained atsubstantially the aforesaid predetermined value.